This invention relates to machine tools which manufacture large quantities of precision parts and more particularly to those which employ perpendicularly mounted slides to feed the tool in the vertical and horizontal directions. In this type of machine, the tool is fed along a path described by predetermined vertical and horizontal movements of the slides to cut the desired precision surface in a workpiece.
In the past, high-production, precision machine tools used an AC motor in combination with a series of belts and pulleys to drive the tool. The motor output drove a shaft having two cams disposed thereon, one controlling the vertical component of the tool path, and one the horizontal. Since the drive was capable of operating the vertical and horizontal cams at only one speed during the actual machining operation, the cams could be rotated at only one speed. Since tool feed rate depends on the rotational speed of the cams and on the slope of the cams, for any given cam the tool could be fed at only one speed.
Feeding the tool at only one speed had several disadvantages. Primarily, production time was lost since the tool had to be fed at the slowest rate which was permitted by the design of the finished part. For example, machining microfinished surfaces, sharp contours or high tolerances requires slower feed rates than machining unfinished surfaces, gradual contours or ordinary tolerances. Thus, a part which had only a single sharp contour with many gentle contours or a single microfinished surface with many non-precision surfaces could be machined only at the slower feed rate permitted by the sharply contoured or microfinished surface, if the machine tool was equipped with only a single feed rate.
Additionally, feed rates could not be adjusted to compensate for excessive tool wear. During some portions of the machining cycle, such as machining a hardened portion of the workpiece or machining a sharp contour, the tool wore at a greater rate than at other portions of the cycle. The faster tools wear out, the more production time is lost replacing worn tools.
By following the present invention, however, the machine tool is able to vary the feed rate during the actual machining operation. Since sharply contoured surfaces or microfinished surfaces can be cut at a slower rate and the gently contoured surfaces or non-precision surfaces can be cut at a faster rate, the part can be made in a minimum amount of time. Additionally, tool wear and machine down-time can be decreased. Thus, a machine tool equipped with a plurality of tool feed rates decreases the production time of each machined part, and increases production rates.
Furthermore, not only are production rates increased by the present invention, but parts are machined with more precise tolerances and microfinishes, with better chip control, i.e. stock removal, and the cam designer is given more flexibility so that a better quality machine part may be produced more efficiently. Thus, a high-production, precision machine tool which is capable of feeding the tool at various rates during each cycle is of major benefit in the machine tool art.